The present invention relates to piezoelectric systems, and more particularly to a generally tubular shaped, coriolis force drive, piezoelectric gyroscope system, and method of its use. The primary embodiment of said present invention system is of a generally elongated tubular shape having inner and outer radially polarized annular region defining surfaces, with an inner electrode present on the inner surface thereof, and four electrodes on the outer surface, said four electrodes on the outer surface ideally being oriented at substantially ninety degree intervals. In use said system is caused to rotate about an essentially centrally located longitudinally oriented axis while a flex inducing driving voltage is applied across two of said four electrodes which are oriented substantially 180 degrees with respect to one another, while an output voltage which is related to the rotation rate is sensed across the other two electrodes.
Piezoelectric gyroscopes are well known in the art. For instance, generally elongated rectangular solid shaped Piezoelectric gyroscopes which serve to produce a voltage at sensing electrodes thereof which is proportional to an angular rotation velocity of said piezoelectric-gyroscope about a longitudinally oriented axis therethrough are known, in which the mechanism of operation involves Coriolis force mediated flexure in a direction which is perpendicular to both said longitudinal axis, and a direction of an applied driving voltage effected flex.
One known embodiment of a piezoelectric gyroscope, as viewed in front elevational cross-section, typically has, at one longitudinally disposed side thereof, two vertically stacked, (ie. one atop the other), regions of vertically oriented polarized direction material sandwiched between driving voltage electrodes attached thereto at upper and lower surfaces. One of said vertically stacked regions of vertically oriented polarized direction material has an upward polarized direction and the other a downward polarized direction. On an opposite longitudinally disposed side thereof, and as viewed in side elevation there are present two adjacent regions of horizontally oriented polarized direction material, (ie. one in front of the other as viewed in frontal elevation), sandwiched between sensing voltage electrodes attached thereto at front and back vertically oriented surfaces. One said adjacent region of horizontally oriented polarized direction material having, as viewed from atop thereof, a horizontal laterally to the right projecting polarized and the other said adjacent region of horizontally oriented polarized direction material having a horizontal laterally to the left oriented polarized direction. That is, the polarized plane and polarized directions on said second longitudinally disposed side are simply rotated ninety (90) degrees, (eg. horizontally oriented), from the plane of the polarized directions, (eg. vertically oriented), on said first laterally disposed side about said longitudinally oriented axis therethrough.
Another prior art embodiment of a piezoelectric gyroscope is comprised of a long solid but flexible elongated rod with piezoelectric ceramics affixed thereto on side faces thereof. Said long solid but flexible rod can be triangular or rectangular in cross-section and have three or four electrodes mounted on side faces thereof. Where only three electrodes are present, both driving and sensing circuits share on of the electrodes. References which describe such piezoelectric gyroscope systems are, respectively:
xe2x80x9cVibrating Angular Rate Sensor May Threaten The Gyroscopexe2x80x9d, Gates, Electronics, 41, 103-134 (1968); and
xe2x80x9cPiezoelectric Vibratory Gyroscope Using Flexural Vibration Of A Triangular Barxe2x80x9d, Fujishima et al., IEEE 45th Annual Symp. On Frequency Control, 261-265 (1991).
Another prior art embodiment of a piezoelectric gyroscope is comprised of a solid but flexible, long, circular cross-section, piezoelectric elongated rod, with multiple electrodes affixed on the outer surface thereof. Such an embodiment is described in U.S. Pat. No. 5,336,960 to Fujishima et al., which is titled xe2x80x9cGyroscope Using Circular Rod Type Piezoelectric Vibratorxe2x80x9d.
Another prior art embodiment of a piezoelectric gyroscope is comprised of a short flexible tubular shaped element, to an outer surface of which are affixed numerous piezoelectric ceramics. Application of driving voltage across some electrodes thereof cause a shape change from essentially circular cross-section toward essentially elliptical cross-section, which shape change, in combination with rotation effected Coriolis force, causes an output voltage to appear at other of said electrodes. Such a gyroscopic system is described in xe2x80x9cThe Dynamics Of A Thin Film Piezoelectric Cylinder Gyroscopexe2x80x9d, Burdess, Proc. Inst. Mech. Engrs. 200 (C4), 271-280 (1986).
Yet another prior art embodiment of a piezoelectric gyroscope is described in an article by the inventor herein, titled xe2x80x9cA Cylindrical Shell Piezoelectric Gyroscopexe2x80x9d, Yang, Intl. J. of App. Electromagnetics and Mechanics, 8, 259-271, (1997). Said article describes a short tubular shaped piezoelectric gyroscope system in which radial and torsional vibration modes are utilized to realize a rotation detecting system.
Disclosed in a related Application by the present Inventor, (Ser. No. 09/271,791), is a piezoelectric gyroscope system comprising a generally longitudinally elongated three dimensional mass of piezoelectric material having first and second longitudinally disposed sides, said piezoelectric gyroscope system being distinguished in that a sensing electrode is present at one terminal end thereof, said sensing electrode being affixed so that it is oriented other than on a longitudinally oriented side of said piezoelectric gyroscope. Typically, said terminal end of said present invention piezoelectric gyroscope system, whereat said sensing electrode is affixed, is accurately described as oriented in a direction perpendicular to the direction of longitudinal elongation, and the generally longitudinally elongated three dimensional mass of piezoelectric material is a selected to be of a rectangular solid shape. Said invention couples the voltage amplification benefits of piezoelectric (Rosen) transformers to the angular velocity measuring capabilities of piezoelectric-gyroscopes, by placing a sensing electrode in a piezoelectric- gyroscope much as is done in piezoelectric-transformers, (eg. as viewed in elevation, at a vertically oriented end of a longitudinally disposed side of a present invention piezoelectric-gyroscope at which is present two regions of horizontally longitudinally oriented polarized direction material). That is, the two sensing electrodes in a conventional piezoelectric-gyroscope, described above as adjacent to regions of horizontally, laterally oriented polarized direction material, (ie. one in front of the other as viewed in frontal elevation), sandwiched between sensing voltage electrodes attached thereto at front and back surfaces, are, in the preferred embodiment of the present invention, replaced by a single electrode at a vertically oriented end of the longitudinally disposed side of the present invention piezoelectric-gyroscope at which is present the two adjacent regions of horizontally longitudinally oriented polarized direction material. Said single electrode can reference to one of the driving electrodes, or to a second sensing electrode. A preferred embodiment of said related invention Piezoelectric Gyroscope, which serves to couple the voltage amplification benefits of piezoelectric (Rosen) transformers to the angular velocity measuring capabilities of conventional piezoelectric gyroscopes, can be described as comprising a generally elongated, typically rectangular solid shaped block of piezoelectric material having first and second longitudinally disposed sides and a longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed side to said second longitudinally disposed side thereof. At the first longitudinally disposed side thereof there are present two, vertically stacked, regions of oppositely oriented polarized direction material sandwiched between driving voltage electrodes. One of said vertically stacked regions of oppositely oriented polarized direction material has, for instance, an xe2x80x9cupwardxe2x80x9d polarized direction and the other a xe2x80x9cdownwardxe2x80x9d polarized direction. And on the second longitudinally disposed side thereof there are two adjacent regions of oppositely oriented polarized direction material, one said adjacent region of oppositely oriented polarized direction material having, for instance, a longitudinally xe2x80x9cto the rightxe2x80x9d projecting polarized and the other said adjacent region of oriented polarized direction material having a longitudinally xe2x80x9cto the leftxe2x80x9d oriented polarized direction. The plane of the polarized directions on said second longitudinally disposed side is rotated ninety (90) degrees from the plane of the polarized directions on said first longitudinally disposed side. Said piezoelectric-gyroscope further has a sensing electrode present at a vertically oriented end of the second longitudinally disposed side of the present invention piezoelectric-gyroscope.
Generally, in use Piezoelectric gyroscopes are caused to rotate at an angular rotation velocity about a typically longitudinally oriented axis, which projects essentially centrally therethrough from said first longitudinally disposed side to said second longitudinally disposed side, and a flex effecting voltage is applied across the driving electrodes while an output voltage is sensed across said sensing electrodes. When both angular rotation velocity about said longitudinally oriented axis therethrough, and flex effecting voltage is present across the driving electrodes, it occurs that, (through the mechanism of Coriolis force), a voltage appears at the sensing electrodes which is related to said angular rotation velocity about said longitudinally oriented axis therethrough. Where the angular rotational velocity about said longitudinally oriented axis therethrough is at least an order of magnitude less than is the natural vibrational frequency of the piezoelectric gyroscope material, the output voltage at the sensing electrodes is typically directly proportional to said angular rotational velocity.
It is also known that materials which are well suited for use in Piezoelectric-transformers and gyroscopes are ceramics in which can be effected regions of poled direction by a xe2x80x9cPoling procedurexe2x80x9d. Ceramics are inherently isotropic so that polarization can be determined by application of an electric field across the materials in excess of the coercive field thereof, (which is typically on the order of 1 MV/m), while raising the temperature of the material above the Curie point, and then cooling the material below this point to lock-in the induced domain structure. A reference which describes this procedure is titled xe2x80x9cSmart Structures and Materialsxe2x80x9d, Culshaw, Artech House, (1996).
A with an eye to the present invention a search of Patents was conducted, with the result being that nothing obviating of the present invention system was identified. The most relevant were:
A Patent to Wirt, U.S. Pat. No. 5,495,760 describes a gyroscope with one or more drive cylinders which have single electrodes on the inside and on the outside diameters.
A Patent to Kumada, U.S. Pat. No. 5,912,528 describes a vibrating gyroscope which includes a ring-shaped vibrator having a node.
A Patent to Kananami et al., U.S. Pat. No. 5,874,674 describes a piezoelectric vibratory gyroscope having non-parallel sides.
Additional known Patents which describe angular or rotation measuring systems comprised of piezoelectric material are:
U.S. Pat. No. 3,143,889 to Simmons et al., which provides for electrodes to be present on a piezoelectric material on top and bottom surfaces and on front and back surfaces.
U.S. Pat. No. 3,258,617 to Hart describes a piezoelectric system which positions sensing electrodes, (see (23) and (24) of FIG. 2 therein), at both the ends of a preferably rectangular shaped mass of piezoelectric material.
U.S. Pat. No. 3,141,100 to Hart describes a rather complex system comprised of a plurality of crystal quartz elements.
U.S. Pat. No. 5,837,895 describes a vibrating gyroscope including a piezoelectric substrate having two divided electrodes on one main surface, and a single electrode on the other main surface.
U.S. Pat. No. 5,942,839 describes a piezoelectric vibratory gyroscope having three parallel vibrator arms.
U.S. Pat. No. 5,912,524 to Ohnishi et al. describes a vibratory gyroscope.
U.S. Pat. No. 5,847,487 to Maeno describes a cross-shaped vibration gyroscope.
U.S. Pat. No. 5,945,600 to Touge et al., describes an angular rate detector.
U.S. Pat. No. 5,767,405 to Bernstein et al., describes a tuning fork gyroscope.
U.S. Pat. No. 5,691,595 to Tomikawa et al., describes a vibratory gyroscope including a planar elastic vibrator having vibrator piezoelectric material layers on the front and back sides.
Additionally:
U.S. Pat. No. 3,736,446 to Berlincourt et al., describes a piezoelectric transformer with an electrode (17) at an end of a preferably rectangular shaped mass of piezoelectric material. This Patent also shows a system structure with various regions of polarized direction material present therein. Reference to FIG. 1 therein shows two regions (13) and (14) of oppositely directed vertical polarized at the leftmost side thereof as viewed in said FIG. 1, and with a region of horizontally polarized material at the right side (12) as so viewed.
U.S. Pat. No. 5,504,384 to Lee et al., shows another piezoelectric transformer with electrodes (11) and (12) at ends of an essentially rectangular shaped block of piezoelectric material. Also described are various regions of polarized material present therein. Reference to FIG. 2 in said 384 Patent shows horizontally oppositely directed regions of piezoelectric material at laterally disposed ends of the essentially rectangular shaped block of piezoelectric material, with oppositely directed vertically poled regions of piezoelectric material centrally located therewithin.
Articles which describe conventional Piezoelectric transformers and gyroscope are:
A paper titled xe2x80x9cPiezoelectric-Ceramic Cylinder Vibratory Gyroscopexe2x80x9d, by Ĥbe et al., Jpn. J. Appl. Phys., Vol. 31, (1992), describes a piezoelectric gyroscope with a cylindrical structure.
Another paper titled xe2x80x9cConsideration On Equivalent Mechanical Circuits For Vibratory Gyroscopexe2x80x9d, by Kudo et al., IEEE Ultrasonics Symp., (1990) described equations of gyro-motion and proposes many vibratory gyroscopes including one utilizing rotation motion in a double resonate vibrator system.
Another paper titled xe2x80x9cPiezoelectric Vibratory Gyroscope Using Flexural Vibration Of A Triangular Barxe2x80x9d, by Fujishima et al., IEEE Forth-Fifth Annual Symp. on Freq. Control. (1991), describes basic principals of a piezoelectric vibratory gyroscope and discloses development of a unique triangular bar flexural vibratory piezoelectric gyroscope.
A paper titled xe2x80x9cMathematical Theory Of The Fork-Type Wave Gyroscopexe2x80x9d, Ulitko, IEEE International Frequency Control Symposium, (1995) describes operation of Fork-type gyroscopes.
Another paper which describes Fork-type Vibratory Gyroscopes is titled xe2x80x9cLiTaO3 Crystal Fork Vibratory Gyroscopexe2x80x9d by Wakatsuki et al., IEEE Ultrasonics Symposium, (1994).
Another paper titled xe2x80x9cFinite Element Analysis Of A Quartz Angular Rate Sensorxe2x80x9d, ANSYS Conference Proceedings, 3.35-48, (1989) is further cited as is a paper titled xe2x80x9cFinite Element Analysis Of Single Crystal Tuning Forks For Gyroscopesxe2x80x9d, by Kudo et al., IEEE Intl. Freq. Control Symp., (1996), describes the results of applying finite element analysis to tuning fork gyroscopes.
Even in view of the identified known prior art, there remains need for new piezoelectric gyroscope systems which provide angular velocity measuring capacity.
In a very broad sense, the present invention can be described as a piezoelectric gyroscope system comprising a generally longitudinally elongated essentially tubular structure presenting with inner and outer annular region defining surfaces and first and second longitudinally disposed ends, said piezoelectric gyroscope system being distinguished in that:
a. an electrode is present on the inner surface thereof, and
b. in that there are present four electrodes on the outer surface thereof spaced at substantially ninety degree intervals, and
c. In that said generally longitudinally elongated essentially tubular structure, the annular region thereof of which is made of piezoelectric material which is radially polarized.
Note that the electrode which is present on the inner surface of the present invention piezoelectric gyroscope system is present to functionally serve as a second plate with respect to driving electrodes, (see electrodes A and C in FIG. 1a), and sensing electrodes, (see electrodes B and D in FIG. 1a. Said electrode is typically present on substantially the entire inner surface, which is to be interpreted based upon said functional purpose of said xe2x80x9cinner electrodexe2x80x9d. Functionally, said inner electrode can be primarily present only directly opposed to said driving and sensing electrodes.
It is noted that the four electrodes on the outer surface thereof can alternatively be described as each being present in a separate quadrant, (as the piezoelectric gyroscope generally longitudinally elongated essentially tubular structure is viewed in cross-section), with at least the two xe2x80x9cdriving electrodesxe2x80x9d thereof being substantially oriented at substantially 180 degrees with respect to one another. The sensing electrodes are, however, also preferably oriented at substantially 180 degrees with respect to one another to optimize sensed voltage magnitude.
In use said piezoelectric gyroscope is caused to rotate at an angular rotation velocity about said longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed end to said second longitudinally disposed end, and a flex effecting voltage is applied across two electrodes oriented at substantially 180 degrees with respect to one another, (ie. driving electrodes) while an output voltage is sensed at the other two electrodes, (ie. sensing electrodes). The end result is that when both:
angular rotation velocity about said longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed end to said second longitudinally disposed end, and
flex effecting voltage is applied across the driving electrodes,
it occurs that, through the mechanism of Coriolis force, another flex perpendicular to the voltage effected flex occurs and is related to said angular rotation velocity about said longitudinally oriented axis therethrough, appears across the two sensing electrodes which are oriented such that the xe2x80x9caxisxe2x80x9d thereof, (ie. the direction through the sensing electrodes and perpendicular thereto), is substantially perpendicular to both the axis of rotation and the xe2x80x9caxisxe2x80x9d of the driving electrodes.
It is also disclosed that the preferred piezoelectric material from which the generally longitudinally elongated essentially tubular structure is made is ceramic, because, as alluded to in the Background Section of this Disclosure, ceramic is inherently isotropic and it is relatively easy to induce polarized regions therein. However, use of any functional material is to be considered within the scope of the present invention, with another very relevant candidate being, for instance, lithium niobate.
A method of monitoring an angular rotation velocity comprises the steps of:
a. providing a present invention piezoelectric gyroscope as just described;
said method further comprising in a functional order the steps of:
b. causing said piezoelectric gyroscope to rotate about a longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed end to said second longitudinally disposed end and applying a flex effecting voltage across two electrodes oriented at substantially 180 degrees with respect to one another, (ie. driving electrodes), such that an output voltage is developed at the other two electrodes, (ie. driving electrodes);
c. monitoring said developed output voltage at said other two electrodes, (ie. sensing electrodes), said monitored output voltage being related to said angular velocity of rotation about said longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed end to said second longitudinally disposed end.
The present invention also includes a tuning-fork shaped piezoelectric gyroscope system comprising an essentially tubular structure made of piezoelectric material presenting with inner and outer annular region defining surfaces, first and second legs thereof being projected from a base, preferably formed from a substantially xe2x80x9cUxe2x80x9d shape tubular structure, said piezoelectric gyroscope system being distinguished in that:
an electrode is present on the inner surface thereof, and
in that there are present two electrodes on the outer surface of each leg, said two electrodes being positioned at substantially 180 degrees to one another and such that an axis through the electrodes on one leg is oriented essentially 90 degrees to an axis through the electrodes on the other leg, and
in that said tubular structure annular region piezoelectric material is substantially radially polarized;
such that causing said piezoelectric gyroscope to rotate about said base and applying a flex effecting voltage across two xe2x80x9cdrivingxe2x80x9d electrodes oriented at substantially 180 degrees with respect to one another on one leg causes an output voltage to develop which can be sensed at the two xe2x80x9csensingxe2x80x9d electrodes on the other leg.
A method of monitoring an angular rotation velocity comprises the steps of:
a. providing a present invention tuning-fork shaped piezoelectric gyroscope system as just described;
said method further comprising in a functional order the steps of:
b. causing said piezoelectric gyroscope to rotate about said base point and applying a flex effecting voltage across two electrodes on one leg thereof which are oriented at substantially 180 degrees with respect to one another, (ie. driving electrodes), such that an output voltage is developed at the two electrodes, (ie. driving electrodes), on the second leg thereof.
c. monitoring an output voltage at said two electrodes, (ie. sensing electrodes), on said second leg, said monitored output voltage being related to said angular velocity of rotation about said longitudinally oriented axis which projects essentially centrally therethrough from said first longitudinally disposed end to said second longitudinally disposed end.
The present invention will be better appreciated, by reference to the Detailed Description Section of this Disclosure, with appropriate reference to the accompanying Drawings.
It is therefore a primary purpose and/or objective of the present invention to teach a piezoelectric gyroscope, and method of its use, said piezoelectric gyroscope comprising a generally longitudinally elongated essentially tubular structure presenting with inner and outer annular region defining surfaces, and first and second longitudinally disposed ends, said piezoelectric gyroscope system being distinguished in that:
an electrode is present over the inner surface thereof, and
in that there are present four outer electrodes on the outer surface thereof, each being present in a separate quadrant, (as the piezoelectric gyroscope generally longitudinally elongated essentially tubular structure is viewed in cross-section), with at least the two xe2x80x9cdriving electrodesxe2x80x9d thereof being substantially oriented at substantially 180 degrees with respect to one another, and
in that said generally longitudinally elongated essentially tubular structure annular region is made from piezoelectric material, preferably ceramic, which is radially polarized.
It is a further objective and/or purpose to teach a tuning fork shaped piezoelectric gyroscope and method of its use, said tuning fork shaped piezoelectric gyroscope comprising an essentially tubular structure made of piezoelectric material presenting with inner and outer annular region defining surfaces, first and second legs thereof being projected from a base point, (preferably a xe2x80x9cUxe2x80x9d shaped base point), said piezoelectric gyroscope system being distinguished in that:
an electrode is present on the inner surface of said legs thereof, and
in that there are present two electrodes on the outer surface of each leg, said two electrodes being positioned at substantially 180 degrees to one another and such that an axis through the electrodes on one leg is oriented essentially 90 degrees to an axis through the electrodes on the other leg, and
in that said tubular structure annular region piezoelectric material is substantially radially polarized;
Other purposes and/or objectives of the present invention will become apparent form a reading of the Specification and Claims.